The present invention relates generally to a data collection system with remote units for telemetrically transferring data to a central processing location, and more particularly, to an automatic meter reading (AMR) system in which conventional subscriber telephone lines are used to transfer collected data (e.g., utility meter readings) from a customer""s premises to a central processor.
A traditional way to collect data from utility meters (e.g., gas, electric, water) at customer sites is to send a person to read the respective meters periodically. An automatic meter reading (AMR) system, as illustrated in FIGS. 1A and 1B, changes this labor intensive data collection procedure. With an AMR system, utility companies not only can reduce the number of necessary meter reading personnel, but also can get more information from the meters. For instance, an AMR system can be set to record the meter data every 15 minutes or so and store the data in memory. A processing center or host computer can then periodically retrieve and analyze the collected data, such that the information may be used to compile peak time and maximum usage statistics, to work with a customer to establish rates, to notify the customer if an abnormal usage is identified, and ultimately to provide better customer services.
Since telephone infrastructure has been established for many years and reaches almost every corner of the country, it is one of the logical choices to use as the AMR system communication means. A typical AMR system configuration is shown in FIG. 1A where a utility company (or meter reading service) utilizes a host computer system 4 to collect data from a plurality of consumers (homes, apartments, businesses, etc.) over the existing telephone system. In certain applications, the host computer system may be co-resident with a telephone central office switch 6 or it may be remotely located (as shown), appearing as just another subscriber telephone line 8 to the central office switch 6. At each consumption point, a telephone line telemetry device 10 is connected to one or more utility meters (not shown), thereby making the meters electronically accessible to a host computer system via the existing public telephone network.
As shown in more detail in FIG. 1B, the design of telemetry device 10 is such that it operates over the same telephone line 8 as the subscriber""s telephone set 12 so there is no need for additional phone lines or infrastructure. In AMR applications, the telemetry device 10 is called a meter interface unit (MIU) or telemetry interface unit (TIU), since the device serves as an interface between two different electrical environments. One side of MIU telemetry device 10, called the meter side, is connected to one or more utility meters 14, 16, 18, while the remaining side of the MIU is connected in parallel across the subscriber telephone line 8. With regard to the telephone-line-side of the MIU, the connection is electrically equivalent to the homeowner plugging in an additional telephone or answering machine, and telemetry device 10 appears in parallel with the other telephone devices 20 which are connected to the phone line. As shown in FIG. 1B, other than connecting MIU 10 to the subscriber line, no modification of the existing telephone line wiring is required.
The MIU telemetry device 10 can be designed to share the telephone line in a manner creating no interference for the customer. If a customer is using the phone 12 or the facsimile machine 20, a static off-hook detection system in the MIU device detects that the phone line 8 is not then available, and a call back to the host computer 4 (FIG. 1A) will not occur immediately, even though a scheduled call back time has been reached. Once the phone line becomes available, the device initiates a call to the host computer. The MIU dials automatically pursuant to a calling schedule and availability of the phone line, uploads the accumulated meter data to the host computer, and then turns itself off to again release the phone line. If the customer wants to use the phone while the MIU device is communicating with the host computer, a dynamic off-hook detection system in the MIU detects this and immediately releases the phone line. As a result of these detection systems, the MIU is transparent to the customer during normal operation. Use by the MIU device of a toll-free 800 number to call the host computer and transfer meter data over the existing telephone line infrastructure further ensures that this is a zero impact event to the customer.
Typically, static off-hook detection has been accomplished using a voltage comparator. However, it has proven difficult to isolate the phone side and the meter side of the MIU device because the output from the voltage comparator is a weak DC signal. Moreover, since there are two different phone systems in wide use (24V and 48V), a jumper has to be used to accommodate the different voltages. In the present invention, a new apparatus and method are used to monitor the telephone line conditions. Utilizing a combination of hardware components and the firmware in a microcontroller, the static on/off hook status of the phone line is monitored, and the microcontroller reacts to the sensed information according to predetermined procedures. This new system eliminates the voltage comparator, and since a fixed voltage level is not being detected, the jumper previously needed to accommodate the two prevalent phone systems is no longer necessary.
With respect to dynamic off-hook detection, the present invention likewise utilizes a combination of hardware components (including an optocoupler isolated switch) and the firmware in the microcontroller to monitor both the dynamic on/off hook status and dynamic change of the phone line voltage. Previously, two microcontrollers (one for the phone side of the MIU device and one for the meter side) were needed to handle the isolation problems.
Since the MIU device is physically connected both to utility meters and a telephone line, a certain breakdown voltage ( greater than 1500V) is required between the telephone terminal and the meter terminals. In this device, a high voltage transformer and optocouplers are used to ensure that the breakdown voltage exceeds the requirement.
Accordingly, one object of the present invention is to provide an MIU telemetry device having an improved apparatus and method for detecting the static off-hook status of the telephone line, wherein the detection of a fixed voltage level is not performed.
Another object of the present invention is to provide such an MIU telemetry device which further utilizes an optocoupler isolated switch as part of the components that monitor the dynamic off-hook status of the telephone line.
Yet another object of the present invention is to provide such an MIU telemetry device in which numerous circuit components are shared in the monitoring of both the static off-hook status and the dynamic off-hook status of the telephone line.
In accordance with a preferred embodiment of the present invention, there is provided an MIU telemetry device for collecting information at a remote location and transmitting the information over a telephone line to a host station, the telemetry device comprising a monitoring circuit coupled to the telephone line which periodically generates a voltage signal having an amplitude that is representative of the telephone line voltage, a pulse-generating circuit (comprising a voltage detector and an optocoupler) which converts the voltage signals into a stream of binary signals (wherein each binary signal has either a first logic level or a second logic level, and the binary signals having said first logic level are of variable duration), and a microcontroller which analyzes the stream of binary signals to determine whether the stream has ceased having binary signals of both said first logic level and said second logic level (wherein the telemetry device is prevented from transmitting over the telephone line) and/or whether the respective durations of two non-consecutive binary signals having said first logic level differ by more than a predetermined amount (wherein the telemetry device is required to stop transmitting over the telephone line).